Energy integrated farm operation with recovery of animal feed from food waste

ABSTRACT

A method of operating an energy integrated farm operation with recovery of animal feed from liquid food waste is described and claimed. The method involves extracting methane gas from animal manure and using the methane gas to power an electrical generator. The electricity from the generator and the methane gas itself may be used to operate a dryer. The dryer is used to dry a liquid food waste stream to yield a dry food product. The dry food product recovered has enough nutritional value to be useful as animal feed.

FIELD OF THE INVENTION

[0001] This invention is in the field of farms and farm animals.

BACKGROUND OF THE INVENTION

[0002] A known byproduct of food production is liquid food waste.Typically the material in the liquid food waste stream contains a largeamount of nutrients. It is industry standard practice to “treat” theseliquid food waste streams as waste that needs treatment, prior todisposal.

[0003] On many farms there are “lagoons” and other concentrated holdingareas for liquid food waste streams. When the liquid food waste streamsare placed in lagoons or other storage areas, the nutrients present inthe food waste are in a form such that it is not possible to feed thenutrients to farm animals.

[0004] It would be desirable to develop a process to transform theliquid food waste streams into usable animal feed, without putting somuch energy into the process that the value of the animal feed collectedis less than the value of the energy used to create the animal feed.

SUMMARY OF THE INVENTION

[0005] The instant claimed invention is a method of operating an energyintegrated farm operation with recovery of animal feed from liquid foodwaste, comprising

[0006] providing farm animals;

[0007] providing liquid food waste;

[0008] wherein said farm animals produce manure;

[0009] wherein said manure is processed in a digester such that methanegas is produced, and

[0010] wherein at least some portion of the methane gas produced is usedto generate electricity;

[0011] the improvement comprising that both, or either of, the methanegas produced by the digester and the electricity produced by the methanegas are used to power a dryer that is used to dry said liquid foodwaste;

[0012] wherein the dried food waste is collected for use as animal feed;and

[0013] wherein optionally at least some of the liquid food waste iscontacted with bentonite clay and an anionic polymer prior to the liquidfood waste being dried in the dryer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The instant claimed invention is a method of operating an energyintegrated farm operation with recovery of animal feed from liquid foodwaste, comprising

[0015] providing farm animals;

[0016] providing food waste;

[0017] wherein said farm animals produce manure;

[0018] wherein said manure is processed in a digester such that methanegas is produced, and

[0019] wherein at least some portion of the methane gas produced is usedto generate electricity;

[0020] the improvement comprising that both, or either of, the methanegas produced by the digester and the electricity produced by the methanegas are used to power a dryer that is used to dry liquid food waste;

[0021] wherein the dried food waste is collected for use as animal food;and

[0022] wherein optionally at least some of the liquid food waste iscontacted with bentonite clay and an anionic polymer prior to the liquidfood waste being dried in the dryer.

[0023] The recognition that methane gas is recoverable from animalmanure is at least 194 years old, according to, “From Biodung toBiogas—Historical Review of European Experience” by Cord Tietjen, pp247-259 of the book, Energy, Agriculture and Waste Management, edited byWilliam J. Jewell, © 1975 by Ann Arbor Science Publishers, Inc.:

[0024] It was in 1808 that Humphrey Davy collected methane in hisexperiments with strawy cattle manure kept in a retort in a vacuum. (4).This might be considered the beginning of manure gas research, but Davywas not interested in solving energy problems with natural fuel gas; hisexperiments were directed toward an evaluation of rotten and unrottedmanure for crop production. pp 247-248.

[0025] Farm animals that are capable of producing manure that can beprocessed to generate methane gas include cows, pigs, sheep andchickens. According to the reference book, “Utilization and Recycle ofAgricultural Wastes and Residues,” edited by Dr. Michael L. Shuler, page11, © 1980 by CRC Press, the relative amount of manure produced by eachdifferent species is as follows: dairy cattle produce the most manure,followed by beef cattle, followed by “swine” (swine means ‘a pig or hog’with the term usually being used collectively), followed by sheep andthen laying hens (chickens raised to lay eggs) with the least amount ofmanure being produced by broilers(chickens raised to be eaten). Forexample, one cow, in one year, produces, on average, about one and onehalf tons of manure. In practicing the method of the instant claimedinvention, the preferred farm animals for producing manure to makemethane gas are those animals that produce the most manure. Therefore,the preferred farm animals for producing manure that will be processedto make methane gas are cows and within the category of cows, thepreferred cows are dairy cows.

[0026] According to “Cutting Energy Costs”, from the 1980 Yearbook ofAgriculture, published by the U.S. Department of Agriculture, on page54, “It is estimated that for each 1,000 pounds of body weight of dairycattle, 44 cubic feet of methane containing 26,000 Btu's can be producedeach day.” (Note: Btu stands for “British thermal unit” and a BritishThermal Unit is defined as the quantity of heat required to raise onepound of water one degree Fahrenheit.)

[0027] The processing of animal manure to generate methane gas is aknown technology. See: “Methane Production From Waste Organic Matter”,David A. Stafford, Dennis L. Hawkes and Rex Horton, © 1980 by CRC Press,Inc., “Biomass Gasification”, Edited by T. B. Reed, © 1981 by Noyes DataCorporation and “Lessons Learned from Existing Biomass Power Plants”, G.Wiltsee, February 2000, National Renewable Energy Laboratory, ContractNo. DE-AC36-99-GO10337.

[0028] U.S. Pat. No. 4,100,023 describes and claims a digester andprocess for converting organic matter to methane and fertilizer; U.S.Pat. No. 4,274,838 describes and claims an anaerobic digester fororganic waste; U.S. Pat. No. 4,759,454 describes and claims a manuredigester and power generating system; U.S. Pat. No. 5,096,579 describesand claims an anaerobic digester; and U.S. Pat. No. 6,299,774 describesand claims an anaerobic digester system. European Patent Application No.486140, describes and claims an anaerobic digester and European PatentApplication No. 26619, describes and claims an anaerobic digester fororganic waste.

[0029] The preferred digester is an anaerobic digester. Anaerobicdigestion, also known as anaerobic fermentation, is a biological processby which organic matter is decomposed in the absence of air to yieldmethane (CH₄) and carbon dioxide (CO₂).

[0030] Anaerobic digesters are commercially available fromR(esource).C(conservation).M(anagement). Digesters™ Inc., P.O. Box 4715,Berkeley, Calif. 94704, (510) 658-4466, www.rcmdigesters.com.

[0031] An anaerobic digester is operated by first having liquid manurestreams enter an in-ground tank. The liquid waste decomposes as it movesthrough the tank. The tank is lined with heat pipes to maintain atemperature of from about 25° C. to about 40° C. (from about 77° F. toabout 104° F.). This temperature range is excellent for the developmentof methane producing bacteria. In operating the anaerobic digester inthe process of the instant claimed invention the preferred operatingtemperature is at the high end of the operating temperature range andthe most preferred operating temperature is about 40° C.

[0032] The methane producing bacteria digest the liquid waste. As partof the digestion process, the bacteria release methane gas. Animpermeable cover placed on the digester traps the methane gas. The factthat the methane gas remains trapped within the digester reduces odorsassociated with alternate forms of manure processing such as open lagoondrying and other concentrated holding areas. This reduction of odors isof huge benefit to the farm owner. In fact, this benefit is realizedregardless of what use is eventually made of the methane gas.

[0033] Operation of the anaerobic digester is a skill known to personsof ordinary skill in the art of processing manure in an anaerobicdigester. There is an extensive discussion in the reference, “ResourcePotential and Barriers Facing the Development of Anaerobic Digestion ofAnimal Waste in California”, December 1977, published by the CaliforniaEnergy Commission, P 500-99-002, of both the technological andcommercial factors involved in the setting up and operation of anaerobicdigesters at sites within California. This reference containsinformation about equipment, plant layout and operating parameters foranaerobic digester operations at a number of different farm sites. Thisentire document is to be considered incorporated by reference, into thispatent application.

[0034] In the method of the instant claimed invention, collected methanecan be used as fuel to run the engines that drive generators to produceelectricity and also, or also, as fuel to be burned to power the dryerused to dry the liquid food wastes.

[0035] In addition to supplying electricity, a by-product of electricalpower generation is the heat created by the generator engines. It is anaspect of the “energy-integrated” features of this invention that theheat from these generator engines could be used to provide heat for thewater pipes used in the continued operation of the anaerobic digester.This is an important consideration when operating an anaerobic digesterduring periods of very cold weather. When cold weather is present and ananaerobic digester is being operated, there is a real potential for anunwanted interruption of operation of the digester when the liquidmanure streams become so viscous, because of the cold temperatures, thatit is difficult to transport them through the digester.

[0036] Therefore, it is very useful that this “by-product” generatorheat can be used to further the operation of the anaerobic digester.

[0037] The electricity generated is used to operate the dryers that aredrying the liquid food waste streams so that a dried food product iscreated.

[0038] The collected methane can also be used as a direct fuel for thosetypes of dryers that directly burn methane in order to generate the heatrequired for drying.

[0039] Therefore, the dryer(s) suitable for use in the instant claimedinvention could be operated solely on electricity, operated solely byburning methane for fuel or the dryer could use a combination ofelectricity and methane to generate the necessary heat to dry the foodwaste. The preferred dryer is dependent upon the energy required inorder to dry the liquid food waste. Some of the dryers that could beused could also be configured such that it is possible for them to useso-called “waste” heat produced from the electrical generator to dryselected liquid food wastes.

[0040] The food wastes being processed using this invention typicallyhave enough liquid present in them that they are referred to as “liquidfood wastes”. It is the intent of conducting the method of the instantclaimed invention that these liquid food wastes so dried would beselected such that they contain sufficient nutritional value such thatonce these liquid food wastes are dried, they would become marketabledry food products for use in the animal feed industry.

[0041] It is very common in the food industry to generate liquid foodwaste that still contains usable nutrients. Typical liquid food wastesstreams can come from many different sources. These sources include, butare not limited to, processing facilities for the dairy industry, thecanning industry, the dried cereal industry and other food industries.For purposes of this invention the preferred liquid food waste streamscome from dairy manufacturing plants.

[0042] Typically liquid food waste from dairy manufacturing plants,includes two basic types of streams. The first is milk and/or milkrelated products that simply were not included within the final product.This type of material is considered “virgin” food material. This type ofliquid food waste is considered to be edible at the time of itscreation. The second type of typical liquid food waste stream is“everything else”. That refers to “everything else” that is currentlybeing sent to the wastewater treatment plant is processed. The valuable“food” components of these streams are the protein, fat, and othertraditional nutrients associated with milk and dairy products.

[0043] The ability of the operator of the method of the instant claimedinvention to capture value from these food wastes makes this inventionhighly commercially significant. In fact, the operator can not only makemoney selling dried food waste as animal feed but the operator can alsomake money by collecting fees from the “owners” of the food waste on thetheory that the owners of the food waste would previously have had topay a “waste disposal” fee (known as a “tipping fee” in the industry)for disposal of the food waste; now that the food waste can be convertedinto usable animal feed a similar type of ‘processing fee’ can becharged to the owner.

[0044] There are many types of dryers that can be used to process theliquid food waste according to the method of the instant claimedinvention. The preferred dryer is the dryer described and claimed inU.S. Pat. No. 5,570,517, Slurry Dryer, which patent issued on Nov. 5,1996. U.S. Pat. No. 5,570,517, is incorporated by reference, in itsentirety, herein. The preferred drying system using the preferred dryerwould typically include the following equipment: an “agitated air”(known as an “AGA”) dryer, a variable speed feeding system, a burnersystem, a burner can, a system exhaust fan, an air flow control valve, acyclone separator and a rotary airlock. All of these pieces of equipmentare commercially available from companies that make and supply thesetypes of dryers.

[0045] Additional optional equipment would include a back mixing systemfor hard to handle materials and an air recycle system to recover fromabout 25% to about 60% of the Btu(s) consumed in the drying process. Useof the air recycle system could reduce discharged process air to theatmosphere by from about 85% to about 90%.

[0046] As mentioned previously, the preferred type of liquid food wastestreams are those food waste streams generated by dairy manufacturingplants. These liquid food waste streams are preferred because of theirhigh protein and fat levels, which make dried animal feed made with themto be of a relatively “high” nutritional value. Furthermore, liquid foodwaste streams from dairy manufacturing plants are preferred because,according to the “2000 Statistical Abstract of the United States”, as of1999, there were about 111,000 farms in the United States that had milkcows and there were about 1,258,000 “dairy manufacturing plants” thatwere capable of processing milk and producing milk products, with aconcomitant “production” of liquid food waste; which means this numberof farms with milk cows and dairy manufacturing plants, ensures thatthere would be a “steady supply” of liquid food waste available to beprocessed by the method of the instant claimed invention.

[0047] Certain liquid food waste streams may be such that they aredifficult to dry. These liquid food waste streams may be contacted witha combination of a slurry of bentonite and an anionic polymer asdescribed in U.S. Pat. No. 5,204,007, entitled, “Method of Clarificationof Waste Water for Production of Animal Feeds”, and U.S. Pat. No.5,759,568, entitled, “Method for Producing Animal Foodstuff from Waste”.U.S. Pat. No. 5,204,007 and U.S. Pat. No. 5,759,568 are incorporated byreference, in their entirety, herein.

[0048] The slurry of bentonite and anionic polymer may be added to theliquid food waste stream at any point between the “creation” of theliquid waste stream in the dairy manufacturing plant and the dryeritself.

[0049] The addition of a slurry of bentonite and an anionic polymerwould only be necessary if the liquid food waste stream was relativelyhard to dry. That is why this is an optional, {not required step} in theprocess of the instant claimed invention.

[0050] Bentonite is available commercially from many sources. One suchsource is American Colloid Company, 1500 West Shure Drive, ArlingtonHeights, Ill., (800) 426-5564, (847) 392-4600, www.colloid.com.

[0051] Anionic polymers suitable for use in the instant claimedinvention include emulsion polymers and dry polymers. Suitable anionicpolymers are available from Ondeo Nalco Company, Ondeo Nalco Center,Naperville, Ill. 60563, (630) 305-1000. Because the dried materialrecovered from the dryer is targeted for use as animal feed, anionicpolymers suitable for use in the instant claimed invention should haveGRAS (generally recognized as safe) status. The current list of suitableanionic emulsion polymers with GRAS status, available from Ondeo NalcoCompany, includes Nalco® GR105 (30 mol percent anionic), Nalco® DT 9812(45 mol % anionic) and Nalco® DT 9813 (a 30 mol % anionic high molecularweight polymer). The current suitable anionic dry polymer, with GRASstatus, available from Ondeo Nalco Company, is Nalco® D9818 (35 mol %anionic),

[0052] The following example is presented to be illustrative of thepresent invention and to teach one of ordinary skill how to make and usethe invention. This example is not intended to limit the invention orits protection in any way.

EXAMPLE

[0053] Seaview Farms is a dairy farm with adjacent dairy manufacturingplant, located in western Illinois.

[0054] The farm has a current herd of about 50 dairy cows, with eachcow, producing, on average, about 40 kilograms of manure a day. Thedairy manufacturing plant annually produces about 12 million pounds of amedium desirable type of liquid food waste stream.

[0055] After an on-site visit and survey, the following equipment isinstalled:

[0056] 1. An anaerobic digester, with supporting pumps, tanks andpiping.

[0057] 2. A methane powered electrical generator with support wiring,piping and pumps.

[0058] 3. A partially methane powered dryer suitable for drying a liquidfood waste stream, wherein the electrical power to operate the dryercomes from the methane powered electrical generator and any methanerequired to power the dryer also comes from the anaerobic digester.

[0059] 4. Suitable pumps and piping and tanks such that it is possibleto add a slurry of bentonite and a GRAS anionic polymer to the liquidfood waste stream upon demand. These materials may be added to theliquid food waste stream at any point between their “creation” in thedairy manufacturing plant and the dryer itself.

[0060] The equipment is set up, test run and operated continuously forone solid month. Extrapolating the results, here is what it is possibleto generate if the liquid food waste stream has a total solids contentof about 18% and is dried without addition of bentonite and a GRASanionic polymers. The calculation is that in one year it is possible toproduce about 2.4 million pounds of an about 90% dry animal feedproduct.

[0061] It is anticipated that the dry animal feed product collected forsale will have the following nutritional value: Protein 11-12% Fat 9-10% In vitro DDM (DDM stands for Digested Dry Matter 96% and it is ameasure of how much of the food is able to be used by the consuminganimal.)

[0062] The present method has been described in an illustrative manner.Many modifications and variations are possible in light of the aboveteachings. It is, therefore, to be understood that within the scope ofthe appended claims the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A method of operating an energy integrated farmoperation with recovery of animal feed from liquid food waste,comprising providing farm animals; providing liquid food waste; whereinsaid farm animals produce manure; wherein said manure is processed in adigester such that methane gas is produced, and wherein at least someportion of the methane gas produced is used to generate electricity; theimprovement comprising that both, or either of, the methane gas producedby the digester and the electricity produced by the methane gas are usedto power a dryer that is used to dry said liquid food waste; wherein thedried food waste is collected for use as animal feed; and whereinoptionally at least some of the liquid food waste is contacted withbentonite clay and an anionic polymer prior to the liquid food wastebeing dried in the dryer.
 2. The method of claim 1 in which said farmoperation is a dairy farm.
 3. The method of claim 1 in which said liquidfood waste is liquid food waste from a dairy manufacturing plant.
 4. Themethod of claim 1 in which said liquid food waste is contacted withbentonite clay and an anionic polymer prior to the liquid food wastebeing dried in the dryer.